The present invention relates to a sheet feeding device for feeding print sheet or copy sheet to a printer unit of a printing machine or a duplicator unit of a duplicating machine one by one, and more particularly, to a device in which a plurality of sheets are held in a stacked state within a cassette case, capable of being temporarily depressed when the case is attached to the machine or detached from it, while the positions for depressing operation and the positions of a pair of rollers for feeding the sheet are simultaneously and automatically changeable in accordance with a width of the sheet stacked in the case.
In the cassette type sheet feeding device as mentioned above, bundles of sheet which are different in size, sheet material and sheet type, are stored in separate cassette cases. Those different cassette cases are loaded into the machine body alternatively as required to supply the machine with a desired type of sheet. This type of device is recently widely used because of handiness. This cassette type device has a case insertion compartment provided in the body of the printer or duplicating machine, into which the cassette case carrying stacked sheets is loaded. There are different versions of such cassette type sheet feeding device, one of which has a sheet feed roller and a separator lug.
In more particular, the sheet feed roller is located at the case insertion compartment to feed the sheet forward by its rotational movement in contact with the top sheet of the stacked sheets. The sheet feed roller is carried by a roller shaft provided in the case insertion compartment, which shaft in turn extends transversely across the case compartment substantially at right angles to the direction in which the cassette case is inserted.
On the other hand, the cassette case is provided with a lifting member carrying the underside of the bottom sheet for movement in the direction in which the sheets are stacked. The lifting member is biased by a predetermined biasing member toward the sheet feed roller so that the top sheet is pressed against the feed roller. The cassette case is further provided with a separator lug mentioned above. The separator lug is located at each corner of the front end of the sheet held in stack in the cassette case in the feed direction thereof to engage at least the front and side of the sheet. During feed operation of the sheet feed roller, the top sheet is at its each corner deformed to a curve to allow the top sheet alone to exit. The separator lug is carried by a lug support member which is movable substantially in the same direction as the stacking direction of sheets.
This process of separating and feeding the sheet one by one by means of a separator lug taking advantage of flexibility of the sheet is generally called a lug-separating sheet flexing method.
When loading and unloading of the cassette case in the device mentioned above, if the stacked sheets in the cassette case are brought into contact with the sheet feed roller at the case insertion compartment, the sheet tends to crease, bend, or to be missplaced in the cassette case or will be subject to other inconveniences. It is therefore necessary to keep the sheet and the sheet feed roller out of contact with each other when loading and unloading the cassette case.
To overcome this problem, there has been proposed such an arrangement that the sheet feed roller is movable between a contact position in which it is in contact with the top sheet in the cassette case and a withdrawn position in which it is apart from the contact position at a certain distance, wherein the sheet feed roller is brought into contact with the sheet only during feed operation.
There has also been a proposed arrangement in which part of the outer circumference of the feed roller is cut away in plane to provide a D profile. Thus, the plane surface normally opposes to the top sheet in the cassette case at a certain distance therefrom to avoid contact therewith, while in feeding operation, the cylindrical portion of the D-shaped roller is brought into contact with the top sheet to feed it out.
The former arrangement of moving the feed roller, however, requires a mechanism for movably carrying the feed roller and an extra driving member for driving it, resulting in a complicated structure and therefore an added cost and failuer probability.
In the latter arrangement with a D-shaped feed roller, a steady control of the feed roller home position in which the cutaway plane opposes to the sheet is required, providing one cause of added expense. Also, a certain stroke of feeding movement must be done with the cylindrical portion of the D-shape, requiring a large-size roller. Furthermore, if there are two feed rollers provided, the D cut shape may be different between the two rollers, which will cause skewed feeding, i.e., the sheet being fed out at a slight angle to the horizontal plane.
The lug-separating type sheet feeding device as mentioned above is often provided with feed rollers in pair which are located inside the both sides of the bundle of sheet at a certain distance therefrom. In this case, feeding errors such as sheet jam, double feed and blank feed are apt to occur unless the side face of the sheet is kept at an optimum distance from each sheet feed roller.
In the cassette type sheet feeding device, usually employed a plurality of cassettes for different sheet sizes. In many cases, those multiple cassettes, each carrying stacked sheets of certain size, are alternatively inserted into a common case insertion compartment provided in the body of printer or duplicating machine or the like. In this type of device, the sheet width is changed with every replacement of cassette case. To cope with this change, it is desirable to keep the roller position constant with respect to the both sides of the paper regardless of varying sheet widths.
To this end, there has been a conventional arrangement in which multiple sheet feed rollers in pairs are fixedly mounted on the roller shaft, each pair being located at a distance corresponding to a certain sheet width from each other. In sheet feeding, the pair corresponding to the selected sheet width is picked out of the multiple sheet feed rollers and is brought into engagement with the sheet near the both sides thereof. Here, in order to allow the common case insertion compartment to be shared by as many as sheet sizes as possible, it is necessary to provide as many sheet feed rollers as possible on the roller shaft.
When the above embodiment is to be applied to such configuration of the feeding device, it is difficult to give an enough space for the press-down operating member between those sheet feed rollers on the roller shaft. More specifically, each cassette case usually has a pair of lug support members spaced in accordance with the sheet size on both sides of the sheet, which are movable substantially in the same direction as the sheet stacking direction. The separator lugs are born by those lug support members so that the distance between the pair of support members is changed with change of sheet sizes. To handle this situation, the press-down operating members must be provided in pairs corresponding to the number of sheet sizes, requiring a considerable space to accommodate such multiple press-down operating members. This would then make it necessary to widen the distance between the multiple feed rollers, resulting in a limited number of sheet feed rollers to be mounted on the roller shaft. As a result, the number of cassette cases sharing one case insertion compartment, i.e., the number of sheet sizes will be limited.